Simplify the expression. $(-3r+3)(-r-7)$
Answer: First distribute the ${-3r+3}$ onto the ${-r}$ and ${-7}$ $ = {-r}({-3r+3}) + {-7}({-3r+3})$ Then distribute the ${-r}.$ $ = ({-r} \times {-3r}) + ({-r} \times {3}) + {-7}({-3r+3})$ $ = 3r^{2} - 3r + {-7}({-3r+3})$ Then distribute the ${-7}$ $ = 3r^{2} - 3r + ({-7} \times {-3r}) + ({-7} \times {3})$ $ = 3r^{2} - 3r + 21r - 21$ Finally, combine the $x$ terms. $ = 3r^{2} + 18r - 21$